This invention refers to a combination of a thermooptical phase shift means and an interferometer, where thermooptical refers to the change in the optical properties of a material medium caused by induced temperature changes in the medium.
A thermal-wave is an oscillating or transient temperature disturbance which propagates in a material medium. Thermal-waves are used in thermal-wave imagers which, in general, have powerful capabilities in comparison with most optical imaging instruments, such as microscopes, cameras, etc. For example, they can provide depth-dependent images of thin samples of materials to depths ranging from millimeters to nanometers. Thermal-wave imagers use methods of heating as follows:
a) Contact heating by conduction into the sample from an adjacent heated layer or other element such as a heated wire. PA1 b) Direct heating of the sample layer by optical absorption and accompanying release of heat by this photothermal mechanism. This mechanism also includes heating with microwaves, and radio frequency fields, that is by the general absorption of electromagnetic radiation. PA1 c) Radiative heat transfer from a blackbody heat source positioned accessibly to the sample. PA1 d) Convective heat transfer from a heated fluid adjacent to the sample. PA1 e) Internal heating by passing an electric current through conducting parts of the sample. PA1 f) Heating by chemical reactions or phase changes occuring in the sample. PA1 1) Heat is generated in a sample, thereby establishing a thermal-wave in the sample which carries the thermal-wave image information. PA1 2) The thermal-wave propagates through the sample by conduction and into a thin layer of optically reflective but highly thermally conductive material called the reflector layer. PA1 3) The thermal-wave propagates through the reflector layer and into a condensed-phase medium which is in thermal conductive contact with the reflector layer. This condensed phase medium is called the phase shift medium (PSM). PA1 4) The phase shift medium (PSM) changes temperature as the thermal-wave propagates through it. The change in temperature of the PSM produces an optical phase shift in the probe beam of an interferometer also passing through the PSM, because of a change in the refractive index of the PSM caused by the heating. PA1 5) The probe beam is propagated through the PSM from an interferometer and the said refractive index change in the PSM produces an optical phase shift in the probe beam of the interferometer. PA1 6) The reflector layer optically reflects the interferometer probe beam incident on its surface, and causes the said probe beam to pass twice through the PSM, traversing the PSM along and approximately coincident with the optical axis of the incident probe beam at the reflector layer, but exiting the PSM in a direction opposite to the direction of propagation of the incident probe beam. PA1 7) The phase shift in the optical probe beam is measured using an interferometer, thereby producing an interferogram from which the optical phase shift may be reconstructed. PA1 8) The interferogram is recorded by means of an electrooptic camera or other suitable recording means.